Flareless, or "bite-type" tube fittings are used to make a strong, fluid-tight connection to the end of a conduit or tube. Such fittings typically employ a tapered arrangement to force one or more ferrules against the outer wall of the tube, biting into it to obtain both a proper seal and grip.
An example of one known type of flareless fitting is shown in Crawford U.S. Pat. No. 2,484,815. This patent discloses a tube fitting comprising a coupling body, a coupling nut and a ferrule. The tube is inserted so that it extends substantially axially inwardly beyond the ferrule, through the length of a counterbore which is slip fit about the tube. Tightening of the coupling nut and the tapered arrangement causes the ferrule to be swaged between the tube outer wall and the internal cylindrical surface of the coupling body.
Another type of flareless fitting is shown in Davis U.S. Pat. No. 3,290,069 which differs from the Crawford fitting in that the fitting body lacks a counterbore, so that the tube cannot penetrate much beyond the inner end of the ferrule. The fitting in the Davis patent is particularly advantageous when tubing installations must be made in close-quarter cramped locations because the fitting and the ferrule, which becomes permanently attached to the tubing when the connection is completed, can be more easily separated from the coupling body when repair or replacement work is needed. The tube need be moved or sprung only a short axial distance from the body when it is disassembled or reassembled.
Conversely, the fitting shown in the Crawford patent requires substantially more axial movement when disassembly or reassembly is done, since the tube end must be axially outward of the body cavity before it can be moved aside.
The fitting shown in the Crawford patent has certain advantages if disassembly is not a problem because the angularity and concentricity of the tube relative to the body are less crucial, since the counterbore acts to locate the tube so that it will be properly located and aligned relative to the fitting body. Therefore, less care is needed in seeing that the tube end is cut squarely since the end is farther removed from the end of the ferrule.
In fact, the Crawford fitting effectively requires that the tube extend substantially axially inwardly beyond the ferrule. Otherwise, the swaging action of the ferrule between the tube and the coupling body could cause the end of the tube to collapse resulting in a defective fitting connection. The ferrule described by Davis can be nearly flush with the end of the tube as the teeth of the ferrule are disposed axially outwardly thereof where the tube is less susceptible to collapsing.
It is therefore desirable to have a tube fitting including the advantages of both of the above-described fittings.